David Arthur Bohling

Growth of high quality AlGaAs by metalorganic molecular beam epitaxy using trimethylamine alane

AlGaAs grown by metalorganic molecular beam epitaxy (MOMBE) has been problematic due to oxygen and carbon contamination, particularly when triethylaluminum (TEAl) has been used as the aluminum source. Consequently, we have investigated trimethylamine alane (TMAAl) as a potential replacement for the conventional metalorganic Al sources. AlGaAs films with excellent structural and optical properties have been grown with this source. Photoluminescence intensities from AlGaAs grown by MOMBE at 500 °C using TMAAl are comparable to those from material grown by metalorganic chemical vapor deposition at 675 °C using triethylaluminum (TMAl). Carbon and oxygen levels in MOMBE‐grown AlGaAs are drastically reduced in comparison to similar films grown with TEAl.

Growth of GaAs and AlGaAs by metalorganic molecular beam epitaxy using tris‐dimethylaminoarsenic

Due to the extreme toxicity of AsH3, safer alternatives for III–V epitaxy are highly desirable. In addition, the AsH3 molecule is too stable to decompose on the wafer surface at the temperature and pressure conditions normally used during growth by metalorganic molecular beam epitaxy (MOMBE). This requires the use of high‐temperature cracker cells to decompose the AsH3 to elemental As prior to entry to the growth chamber and as a result leads to significant As buildup within the chamber. In this letter we report for the first time MOMBE growth at low temperatures (≤525 °C) using a novel As precursor, tris‐dimethylaminoarsenic (DMAAs) without precracking. Specular surface morphologies were obtained over a wide range of growth temperatures, 375–525 °C, for both GaAs and AlGaAs. Carbon concentrations measured by SIMS analysis in GaAs layers deposited from triethylgallium were lower than those obtained using a similar flux of AsH3, while carbon was reduced more than two orders of magnitude in films grown with...

Surface reactions of dimethylaminoarsine during MOMBE of GaAs

Abstract We present in-situ mass spectroscopy studies of surface reactions of dimethylaminoarsine and tertiarybutylarsine under metalorganic molecular beam epitaxy conditions. The results show that the thermal decomposition of dimethylaminoarsine is completed at 450°C with the major products being dimethylamine, hydrogen, aziridine and N-methylmethyleneimine. In contrast, tertiarybutylarsine is not fully decomposed even at 550°C. Co-dosing experiments with trimethylgallium and deuterium labeled trimethylgallium (Ga(CD 3 ) 3 ) show methane and methylarsenic to be major reaction products in addition to nitrogen containing species, specifically aziridine, methylmethyleneimine and dimethylamine. No trimethylamine is detected as a surface reaction product. The generation of methane and methylarsenic from the surface is proposed as a possible mechanism for the reduced carbon incorporation reported for molecular beam epitaxy growth of GaAs with dimethylaminoarsine.

Effect of source chemistry and growth parameters on AlGaAs grown by metalorganic molecular beam epitaxy

Abstract We have investigated the effect of V/III ratio and substrate temperature on the growth rate, Al composition, crystallinity, and impurity concentration of AlGaAs grown by metalorganic beam epitaxy (MOMBE). The effect of these growth parameters on the deposition rates of both GaAs and AlAs has also been determined. By comparing films grown from various combinations of triethylgallium (TEGa), trimethylgallium (TMGa), triethylaluminum (TEAl), and trimethylamine alane (TMAA1), we have been able to further identity the surface reactions which are most important in determining film composition and quality.

Alternative group V sources for growth of GaAs and AlGaAs by MOMBE (CBE)

Abstract We have investigated the use of phenylarsine (PhAsH 2 ) and trisdimethylaminoarsenic (DMAAs) as potential replacements for AsH 3 during growth by metalorganic molecular beam epitaxy (MOMBE), alternatively known as chemical beam epitaxy (CBE). PhAsH 2 was found to decompose rather inefficiently on the surface at a growth temperature of 525°C. However, GaAs and AlGaAs growth rates up to ∼ 95 A/min could still be obtained at this temperature without incurring any degradation in morphology. The hydrogen generated by the decomposition of the PhAsH 2 did not appear to getter carbon from the surface as both GaAs and AlGaAs grown from PhAsH 2 contained ten times more carbon than layers grown under the same flux of AsH 3 . By contrast, DMAAs was found to decompose readily on the wafer surface allowing growth rates up to 220 A/min and growth temperatures as low as 375°C. Furthermore, DMAAs was found to getter carbon more efficiently than cracked AsH 3 , probably as a result of tertiary amine formation at the wafer surface. As a result, comparable carbon backgrounds were obtained at 525°C from either TEG or TMG. By using these sources in tandem, it appears that AsH 3 may no longer be required for growth of GaAs or AlGaAs by MOMBE. In addition, these sources allow new flexibility for selective growth as well. The stability of PhAsH 2 allows for selective deposition of pAlGaAs even at temperatures as low as 525°C. While the same effect is not observed for GaAs growth from TEG at these temperatures, it is possible through the use of DMAAs to deposit high purity GaAs selectivity from TMG since the DMAAs getters the carbon without inducing deposition on the mask. Thus the use of PhAsH 2 and DMAAs will allow selective deposition of device structures such as Pnp HBTs at their optimum growth temperature of ∼ 525°C.

Chemical/surface mechanistic considerations in the design of novel precursors for metalorganic molecular beam epitaxy

Abstract In the design of chemical precursors for metalorganic molecular beam epitaxy (MOMBE), the following issues must be considered: the intrinsic decomposition pathways of the source, the interaction of the reactant and products with the interface, and volatility and safety of the precursor. A representative example would be the development of alternative group V metalorganic sources as arsine and phosphine substitutes. The standard sources used in MOMBE in growing GaAs or any other arsenic based III–V material are typically solid arsenic or thermally cracked arsine. Both sources produce As 2 and/or As 4 which then are transported to the growth surface. Although these are used effectively in III–V growth, chemical substitutes are desirable for a number of reasons, including safety, minimization of system corrosion, and selectivity. A number of alternative arsine substitutes have been suggested over the years, but this paper will focus mainly on the mechanistic design considerations of three group V materials; tertiary butyl arsine (TBAs), phenyl arsine (PhAs), and tris-dimethylamino arsenic (DMAAs). Other examples of group III chemical precursors for MOMBE will also be considered.

Growth of AlxGa1−xAs by reduced pressure MOVPE using trimethylamine alane

Abstract High quality epitaxial layers of AlxGa1-xAs have been grown by reduced pressure MOVPE using the new aluminium precursor trimethylamine alane in combination with trimethylgallium and arsine. The layers were grown at 650°C and were shown to possess n-type conductivity for all aluminium compositions. Low temperature photoluminescence data indicated that carbon was still present in the low aluminium content layers. In marked contrast to previous studies at atmospheric pressure, the AlGaAs layers grown at low pressure using trimethylamine alane were of high compositional and thickness uniformity.

Low temperature growth of AlGaAs by MOMBE (CBE) using trimethylamine alane

In order to gain further insight into the surface chemistry of AlGaAs growth by metalorganic molecular beam epitaxy, we have investigated the deposition behavior and material quality of AlGaAs grown at temperatures from 350 to 500°C using trimethylamine alane (TMAA), triethylgallium (TEG) and arsine (AsH3). Though the Al incorporation rate decreases with decreasing temperature, Ga-alkyl pyrolysis, and hence Ga incorporation rate, declines more rapidly. Thus the Al content increases from XAlAs = 0.25 at 500°C to XAlAs = 0.57 at 350°C. Below 450°C, the Ga incorporation rate appears to be determined by the desorption of diethylgallium species, rather than interaction with adsorbed AlH3. Similarly, carbon incorporation is enhanced by ∼ 2 orders of magnitude over this temperature range due to the increasingly inefficient pyrolysis of the Ga-C bond in TEG. Additionally, active hydrogen from the TMAA1, which normally is thought to getter the surface alkyls, is possibly less kinetically active at lower growth temperatures. Contrary to what has been observed in other growth methods, low growth temperatures produced a slight decrease in oxygen concentration. This effect is likely due to reduced interaction between Ga alkoxides (inherent in the TEG) and the atomic hydrogen blocked Al species on the growth surface. This reduction in oxygen content and increase in carbon concentration causes the room temperature PL intensity to actually increase as the temperature is reduced from 500 to 450°C. Surprisingly, the crystalline perfection as measured by ion channeling analysis is quite good, χmin≤5%, even at growth temperatures as low as 400°C. At 350°C, the AlGaAs layers exhibit severe disorder. This disorder is indicative of insufficient Group III surface mobility, resulting in lattice site defects. The disorder also supports our conclusions of kinetically limited surface mobility of all active surface components.

The impact of impurity incorporation on heterojunction bipolar transistors grown by metalorganic molecular beam epitaxy

Abstract It has been well documented that the ability of metalorganic molecular beam epitaxy (MOMBE) to grow heavily doped, well-confined layers of either n- or p-type is a significant advantage for the heterojunction bipolar transistor (HBT). This feature arises primarily from the ability to use gaseous dopant sources in the absence of interfacial gas boundary layers. While the absence of a boundary layer is an advantage for doping, it can be a disadvantage in other areas such as AlGaAs purity. This paper will discuss how these difficulties can be overcome through the use of novel Al or Ga precursors thus allowing deposition of high quality GaAs-based HBTs. The resulting reduction in background impurities and hence compensation allows for the use of lower dopant concentrations in the AlGaAs thus producing significant improvement in the leakage behavior of the base-emitter junction. Even further improvement can be achieved through the use of InGaP. Using novel Ga precursors, such as tri-isobutylgallium (TIBG), the problems associated with the sensitivity of composition to growth temperature are greatly reduced, allowing for the reproducible deposition of device structures containing InGaP emitter layers. In addition to impurity related performance degradation associated with the emitter, degradation over time due to defects or impurities, most likely hydrogen, in the base region has also been observed. The various sources of hydrogen present during growth have been identified suggesting that it may be possible to prevent hydrogen uptake. However, even in structures where hydrogen has been incorporated, a brief in-situ anneal appears adequate to drive off the hydrogen and eliminate the degradation in gain with operating time observed in large-area devices.

The role of aluminum and hydrogen in impurity contamination of AlGaAs grown by MOMBE

Abstract We have investigated the effect of Al in the form of trimethylamine alane (TMAAl), or elemental Al, and hydrogen, bonded to Group III or Group V precursors, on the oxygen and carbon concentrations of AlGaAs grown by metaorganic molecular beam epitaxy (MOMBE). Al was found to increase both the oxygen and carbon incorporation rates relative to GaAs. The primary source of the oxygen has been determined to be alkoxide contamination of the alkyl Group III sources. Similarly, the carbon contamination is due to carbon released from the decomposition of the alkyl Ga sources. For films grown with TEGA, this enhancement of the carbon uptake can be suppressed through the use of TMAA1 which releases atomic hydrogen at the growth surface. Hydrogen does not appear to remove carbon generated from methyl radicals, as AlGaAs grown from TMGa exhibits hole concentrations >10 19 cm −3 . regardless of Al source, which increase with increasing AsH x /As 2 ratio. We have also determined that increasing the AsH x /As 2 ratio does not improve the crystallinity of the AlGaAs layers as determined by ion channelling analysis.